Technical Abstract:
This research effort involved the numerous ARS rangeland and pasture scientists from 9 western states (ND, OK, TX, AZ, CO, WY, MT, ID, OR) in cooperation with the Texas A&M University Blackland Research Center. The project focused on assessment of CO2 flux over intact, unmanaged native rangeland. The Bowen ratio/energy balance (BREB) method was used to measurre CO2 flux, and supporting data included annual precipitation, peak leaf area index (LAI), standing biomass, litter, root biomass, and soil carbon. Leaf area index and precipitation accounted for 83% of the variation in average monthly CO2 flux among sites. Both soil carbon and root biomass were poor predictors of average monthly CO2 flux (soil carbon explained less than 40% of the variation and root biomass less than 10%). Gap-filling procedures have not been completed for all locations. Where annual CO2 flux estimates are available, rangelands appear to be a sink for atmospheric CO2, sequestering 50 to 100 g CO2 m-2 yr-1 on the arid end of the scale (OR - sagebrush), 100 - 300 g CO2 m-2 yr-1 on moist or cooler sites (ID - sagebrush, ND and Ok - mixed prairie), and 1100 g CO2 m-2 yr-1 on the wettest site (TX - tallgrass prairie). Our data suggests that U.S. rangelands are likely a sink for atmospheric CO2.